Science

No mold, no maggots: How to keep your jack-o’-lantern fresh until Halloween

Matt Casson Associate Professor of Mycology and Plant Pathology West Virginia University,


For many Americans, pumpkin means fall is here. In anticipation, coffee shops, restaurants and grocery stores make their debut Pumpkin Flavor Promotions At the end of August, a month before autumn officially begins. And shoppers start buying fresh ornamental winter produce, such as pumpkins and turban squash, on the hot, humid days of late summer.

But these fruits — yes, botanically, pumpkins and squash are fruits — don’t last forever. And if you buy and carve them too early they may not even make it to Halloween.

As a plant pathologist, gardener and self described Pumpkin FanaticOf course, I have courageously succeeded and miserably failed to grow, properly carve, and keep these iconic winter squash in their prime by the end of October. Here are some tips that can help keep your epic carvings until the Day of the Dead.

This jack-o’-lantern has been carved from a pumpkin with a pre-existing fungal disease, southern blight, showing signs of soft rot, especially around the nose and eyes. The round ball-like structures that form inside the eye socket are fungi.

Matt Casson, CC BY-SA


Choose a Healthy Pumpkin and Carry It Carefully

It may sound obvious, but shop for pumpkins the same way you shop for produce. Whether you plan to carve them or not, choose pumpkins that are not damaged, jagged or diseased. Is the stem loose? Are there any obvious breaks in the peel? Are there water-soaked spots on the exterior?

Post-harvest diseases—which occur after a pumpkin has been removed from the vine—can occur anywhere between the area where they were grown and your front step. A scratch or crack will allow opportunistic fungi, bacteria, water molds and small insects to invade and colonize your pumpkin. Keeping the rind blemish free and the stem intact ensures a long shelf life for your prized pumpkin.

soft rot in squash
As the soft rot progresses in diseased squash, the water-soaked appearance spreads and eventually the pulp becomes watery like a baked pumpkin pie.

Matt Casson, CC BY-SA


Home travel also matters. Most of us transport pets, kids, muddy hiking shoes and food in our cars, which makes our vehicles giant petri dishes harboring common environmental mold and bacteria. Some of those microbes may be colonizing your unsuspecting pumpkin.

Secure your pumpkins on their way home so they don’t suffer injury or stem break. My family often uses seat belts to protect us. Once home, don’t store your pumpkin near the stem, which can cause breakage, especially if it’s large and heavy.

keep them clean and dry

Pumpkin spends most of his life in the fields, growing on top of soil that is full of fungi, bacteria, water molds and soil-dwelling animals such as nematodes, insects and mites. Removing these organisms, and any eggs they may have stuck to your pumpkin’s rind, will help preserve it.

To get rid of them, wipe down your pumpkin, preferably with a bleach wipe or two. This is especially important if you plan to carve them: Piercing the dirty rind with a sharp tool will introduce these curious visitors deep into the heart of your pumpkin. Be sure to use clean tools as well. Small amounts of pumpkin debris stuck in the teeth of dirty carving knives can allow microorganisms to reside and multiply.

Even if you’re not carving your pumpkin, it’s not a bad idea to wipe it down, as it may have small sores or cracks that can be easily overlooked.

Hollow the pumpkin thoroughly, but don’t overdo it

Much of the work of carving a pumpkin involves separating the fibrous strands and the seeds inside from the tough pulp that makes up the pumpkin’s walls. When you pull out the inside of the pumpkin, inspect the inside walls thoroughly for soft rotten patches or dark tissue that may have been colonized by bacteria, fungi or water molds before or after harvesting. Have been Diseased pumpkins sometimes produce an unpleasant odor, so use your nose as well.

If you find these issues when carving, you may want to try carving another pumpkin. You can also paint your pumpkin instead of carving it, which doesn’t require peeping inside.

Some online tutorials and YouTube videos recommend thinning the walls of the pumpkin to allow the candle or LED light to pass through better. But if you make the walls too thin, the fangs of your jack-o’-lantern will wilt and deform as the flesh becomes strips of folded skin inward. The toothless jack-o’-lantern doesn’t scare anyone.

Another advantage of thick retaining walls is that it enables you to attempt 3D carving. This involves shaping the surface of the pumpkin as you would a piece of wood without breaking the shell, and can produce dramatic results.

Some people soak their carved pumpkins in diluted bleach or vinegar water after they are done. But this technique is a double-edged sword: Adding more free moisture to your masterpiece invites wind-blown mold spores and rain-hide bacteria to colonize it. However, applying a light coating of petroleum jelly or vegetable oil to all exposed areas can extend the shelf life of your sculpted squash.

mold on a carved pumpkin
Filamentous fungi such as Penicillium are common in many environments, and can even colonize a freshly bleached jack-o’-lantern like the one shown here. Note the small green colonies on the inside of the carved mouth and on the back wall of the pumpkin.

Matt Casson, CC BY-SA


protect your creation

October is a wet month with incessant rain in many parts of the US. The rain that falls on your jack-o’-lantern will invite every mold in the neighborhood to take up residence in or on it. For this reason, I recommend placing your pumpkins on a covered porch or displaying them in a window from indoors.

It’s okay if some mold builds up inside it, as not all fungi cause soft rot—diseases that cause wet spots that spread, become mottled, and blacken. If the pumpkin gets overly moldy on the inside walls, move it outside so your house doesn’t produce too many spores.

When your pumpkin starts to wilt and fall apart, don’t throw it in a landfill. Place it for your neighborhood greens or on top of your compost pile. Or find a spot in your yard where you can see it getting worse over time, until it turns back into soil in time for next year’s pumpkin patch.

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